This investigation has four objectives directed toward continuing the development of the hibernator as a model system for studying the effects of narcotics on central nervous system (CNS) function and for studying the effects of changes in the CNS associated with the hibernation state on the mechanisms underlying the development of physical dependence on and tolerance to narcotics. The first objective is to continue studies begun in the previous project period of the effects of deep hibernation on the nature of physical dependence on morphine in ground squirrels (Citellus lateralis), as determined by the naloxone-precipitated abstinence syndrome. The second objective is to determine the effects on body temperature of systemic or intrahypothalamic injections of morphine in ground squirrels during euthermia (not hibernating). The third objective is to determine the effects on body temperature of intrahypothalamic injections of morphine in ground squirrels during deep hibernation. The fourth objective is to determine the effects of iontophoretically-applied morphine and naloxone on individual hypotalamic temperature-sensitive neurons during euthermia and hibernation.